Tushar 1.6 - Cell division

Question 1

All phases of cell cycle

Answer 1

Interphase - G1, S, G2 - interphase is the metabolically active phase between cell divisions
Mitosis - PMAT
Cytokinesis

Question 2

What happens during G1

Answer 2

• cell grows (rapid protein synthesis) + metabolic reactions
• proteins for DNA synthesis (next stage) are made
• mitochondria and chloroplasts (organelles) are duplicated

Question 3

What happens during S phase

Answer 3

DNA is replicated - still is in the form of chromatin

Question 4

What happens during G2

Answer 4

protein synthesis to make proteins needed for cell division

• chromosomes begin condensing
• preparation for cell division
• duplicate organelles

Question 5

What is chromatin

Answer 5

• DNA is stored as chromatin during interphase
• it is loosely packed DNA
• it allows translation to happen for protein synthesis

Question 6

What is chromosome

Answer 6

• DNA organises into chromosomes for mitosis
• tightly wound and condensed (via super-coiling)
• translation cant happen in this form

Question 7

What are sister chromatids

Answer 7

These are genetically identical strands of DNA that are replicated (in S phase). They are held by centromeres.

Question 8

What is mitosis needed for

Answer 8

• growth
• asexual reproduction
• tissue repair
• embryonic development
• cells also need to divide to maintain large SA:V, cells divide when they reach a certain size

Question 9

What does mitosis do

Answer 9

Produces 2 genetically identical daughter nuclei

Question 10

What happens in prophase

Answer 10

• SNA supercoils, chromatin –> chromosomes
• nuclear membrane breaks down
• spindle fibres completely form by the end of prophase
• centrosomes move to opposite poles

Question 11

What happens during metaphase

Answer 11

• spindle fibres (microtubules) from centrosomes attach to the centromeres (kinetochores) of each chromosome
• microtubule depolymerisation = spindle fibres contract and shorten, this aligns the sister chromatids along the centre of the cell (equatorial plate/metaphase plate)

Question 12

What happens during anaphase

Answer 12

• spindle fibres continue to shorten, causes sister chromatids to separate, now they are referred as chromosomes
• chromosomes pulled to opposite poles

Question 13

What happens during telophase

Answer 13

• spindle fibres dissolve
• nuclear membrane + nucleolus formed
• chromosomes uncoil to chromatin
• beginning of cytokinesis

Question 14

Mitotic index

Answer 14

Number of cells in mitosis/total number of cells

Used to predict how quick cancer could spread + response of cancer cells to chemotherapy

Question 15

Cytokinesis in animal cells

Answer 15

Cytokinesis is the division of cytoplasm

1) Microfilaments (contractile protein) located beneath the cell membrane at the equator pulls the membrane inward
2) this forms a cleavage furrow
3) when cleavage furrow reaches centre, the cell in pinched apart into 2 daughter cells

Question 16

Cytokinesis in plant cells

Answer 16

1) carb rich vesicle form golgi apparatus form a row at the centre of the cell
2) The vesicles fuse, forming an early cell plate
3) Cell plate grows outwards (by more and more vesicles being brought in), and then the cell plate fuses with the cell wall, dividing into 2 daughter cells

Question 17

What are cyclins and how do they work

Answer 17

• cyclins control the progression of the cell cycle
• they bind to enzymes called cyclin-dependent kinases (CDKs)
• when cyclin binds to CDK, activated CDK attaches phosphate group to a target protein in the cell (this is phosphorylation)
• this makes the protein active, the protein will carry out tasks specific to the phase in cell cycle
• after even is done, the cyclin is degraded
• cyclin levels peak when their target protein is required

Question 18

Different types of cyclins

Answer 18

Cyclin B: triggers move from G0 to G1 and G1 to S
Cyclin E: prepares cell from DNA replication in next phase
Cyclin A: activates DNA replication in S phase
Cyclin B: promotes assembly of mitotic spindle + preparation for mitosis

Question 19

what is tumor and different types

Answer 19

tumor: abnormal cell growth resulting from uncontrolled cell division
benign tumor: tumor that does not spread to other parts of the body
malignant tumor: tumors that can spread to other parts of the body (cancer)

Question 20

What are mutagens

Answer 20

Agents that cause mutations
 Mutagens can be:
 - physical: radiation
 - biological: viruses
 - chemical: e.g. arsenic

most mutagens are carcinogens (mutagens that lead to cancer)

Question 21

Oncogenes

Answer 21

are mutated genes that contribute to the development of a tumor

• proto-oncogene: stimulate cell cycle + growth, cancer occurs when proto-oncogenes are mutated
• tumor suppressor gene: gene that goes against cell cycle and causes cell death (prevents cancer)

Question 22

What is metastasis

Answer 22

• movement of cells from a primary tumor to other parts of the body where they develop into secondary tumors
• secondary tumors are made of same types of cells as primary tumors

1) cancer cells detach from primary tumor
2) they can the ability to penetrate walls of vessels to circulate around the body
3) circulated cells invade different tissues and develop into secondary tumors by mitosis

Question 23

Smoking and cancer

Answer 23

strong positive correlation between frequency of smoking and development of cancer

cigarette smoke has many carcinogens